Loudspeaker



S. WALCZAK June 4, 1963 LOUDSPEAKER 2 Sheets-Sheet 1 Original Filed Dec. 3, 1956 I N VEN TOR. SYLVESTER NAI-[ZAK United States Patent 3,992,694 LGUDSEEAKER Sylvester Walezak, Egg Harbor City, NJ, assignor to Radio Corporation of America, a corporation of Delaware Continuation of application Ser. No. 626,011, Dec. 3, 1956. This application Feb. 16, 1959, Ser. No. 793,631 13 (Ilaims. (Q1. 179115.5)

The present invention relates to electromechanical and electroacoustical transducing apparatus and the methods for the assembly of such apparatus, and more particularly to improved magnetic structures of simple and economical construction for a transducer, such, for example, as a loudspeaker and the methods of assembly of such structures and structures of a similar type.

This application is a continuation of my application Serial No. 626,011, filed December 3, 1956 and now abancloned.

Previous eiforts have been directed toward providing simple and economically assembled magnetic structures for loudspeakers. United States Patent No. 2,501,032 discloses a loudspeaker magnetic structure wherein the portions of the structure, which define the air gap for receiving the voice coil, are accurately positioned with respect to each other and anchored in place by means of a single member. This member is illustrated in the patent as a centering ring which surrounds a pole piece disposed centrally in an aperture in the pole plate of the yoke structure. This centering ring centers the pole piece in the aperture so as to accurately define the air gap, and is constructed to exert spring forces on the pole piece so as to anchor it securely in the yoke structure. -In another attempt to simplify loudspeaker magnetic field structure construction, a single strip of magnetic material has been used to form an integral yoke structure and pole plate thereby replacing separate pole pieces which are conventionally fastened to the yoke structure on assembly of the loudspeaker magnetic structure.

Briefly described, the present invention provides improvements in loudspeaker magnetic structures and improved methods for the assembly of such structures. The magnetic structure includes a yoke structure that may be an integral yoke and pole plate. The portion of the yoke structure in back of the pole plate is maintained initially in open position so that the magnet element of the magnetic structure, which are enclosed by the yoke, may be easily inserted therein. This element may include a pole piece which cooperates with the front or pole plate portion of the yoke to define the air gap. A single member is provided for positioning the enclosed portion of the magnetic structure with respect to the yoke so that it is properly disposed in the air gap. This member is constructed so as to have spring characteristics. When the back portion of the yoke structure is closed, the positioning member is compressed thereby applying spring forces to the enclosed portion of the magnetic structure to anchor the portion in its proper position. Thus, the magnetic structure and improved assembly methods of the invention permits permanent assembly in a single closure operation. The structural arrangement of the parts insures proper alignment of parts and prevents over compression of the positioning member. Rejects are therefore minimized.

It is, therefore, a primary object of the invention to provide a loudspeaker magnetic structure of simple and economical construction, and an improved method of assembly of such structure.

It is an auxiliary object of the invention to provide a loudspeaker magnetic structure combining the features of an integral yoke structure and single centering mem- Patented June 4, 1963 "ice be r and to provide a simplified assembly method for such a loudspeaker magnetic structure, thereby lowering manufacturing costs.

It is another auxiliary object of the invention to provide loudspeaker magnetic structures that can be assembled rapidly with a minimum number of rejects and to provide improved methods for the assembly of such structures.

It is a further object of the present invention to provide a loudspeaker magnetic structure of high quality and improved performance that is lower in cost than magnetic structures heretofore available, and to provide an improved method of loudspeaker magnetic structure assembly.

The novel features of the invention, as well as additional objects and advantages thereof, will be understood more fully from the accompanying description when read in connection with the accompanying drawings, in which:

FIGURE 1 is a fragmentary, exploded view showing, in perspective, portions of a loudspeaker incorporating a magnetic structure constructed in accordance with the invention;

FIGURE 2 is a sectional view, in elevation, of portions of a loudspeaker including the magnetic structure shown in FIG. 1 prior to the final assembly thereof; and

FIGURE 3 is a sectional view, in elevation, of portions of a loudspeaker including the magnetic structure shown in FIG. 1, positioned in apparatus for performing another step in the assembly thereof.

Referring to the drawings, and particularly to FIG. 1 thereof, there is shown a magnetic structure 2 for a loudspeaker incorporating the present invention. This magnetic structure 2 is mounted, for example, by spot welding techniques, upon a housing 4 in which the diaphragm or cone of the loud-speaker will be located. This housing is referred to in the art as the dishpan of the loudspeaker.

The magnetic structure 2 includes a yoke 6 of magnetic material, such as cold rolled steel. This yoke is shown in the drawings as being formed of a band or strip in integral portions. 'Ihese portions include a pole plate 8, side plates 10 and 12, and a back plate 14. The band is formed into a rectangular shell to provide the yoke 6. The pole plate 8 is fastened to the dishpan '4. This pole plate has a circular aperture 16 therein and an internal groove 18 surrounding and concentric with the aperture 16. As will be brought out hereinafter, the surfaces of the aperture 16 will cooperate in defining the air gap of the magnetic structure. The yoke 6 is bent in the form of a substantially rectangular shell. The shell is closed except at the corner defined by the junction of the side plate 12 and .the back plate 14. It will be observed that the back plate 14 is bent at an angle with respect to the other of the side plates 10. The back plate 14 is initially disposed above the end of the side plate 12. Upon assembly, the back plate 14 will be bent downwardly toward the pole plate 8 so as to engage the side plate 12. The engaging ends of the back plate 14 and the side plate 12 are dovetailed so as to lock in place when the structure is assembled.

The illustrated yoke structure 6 may be formed by stamping and punching operations. The aperture 16 may be punched and the groove 18 may be formed in a stamping operation. The dovetail parts may be punched. The dovetail is provided by a tongue on the free end of the back plate and a groove on the free end of the side plate 12. It will be appreciated that the principles of the present invention may be incorporated in magnetic structures using yokes formed of individual, rather than integral portions. It will be desirable, in constructing the yoke structure 6, to make the height of the individual plates 10 and 12 equal as measured from the pole plate 8 damage to other parts of the magnetic structure 2.

A cylindrical permanent magnet 20 is enclosed within the yoke structure 6. This magnet may be of the type which is constituted of an alloy or aluminum, cobalt, nickel and iron. A pole piece 22 may be a cylindrical body of soft magnetic material, such as iron, having a flange 26 which is disposed in abutting relationship to the magnet 20. The flange 26 forms a shoulder of the body of the pole piece. The pole piece 22 and the magnet 20 comprise the pole element of the magnetic structure. The pole piece 22 is adapted to be inserted into the aperture 16. The peripheral surface of the pole piece 22 and inner annular surface of the aperture 16 define an annular air gap for the magnetic structure. This air gap will receive the voice coil of the loudspeaker.

. The pole piece :22 is desirably accurately centered Within the aperture 16 in order to accurately define the air gap. To this end, a centering member 24 of nonmagnetic material, such as phosphor-bronze or brass, is provided. This centering member is in the nature of a ring having a cylindrical side portion or flange and a disklike :top portion or Web. The top portion of the centering member 24 is somewhat corrugated so as to enhance its action as a spring. The centering member 24 functions both as a centering member and as a compression spring. Consequently, it will be referred to herein as a comp-ression-centering member. The bottom of the cylindrical portion of the compression-centering member 24 is inserted in the groove .18'that is formed in the pole plate 8. Since the groove 18 is concentric with the pole plate aperture 16, it provides a seat :for' the compression-centering member 24, which seat is centered with respect to the aperture 16. Thus, the compression-centering member 24 is centered with respect to the pole plate aperture 16 when disposed in its seat. The unattached end of the disk portion of the compression-centering member 24 bears .upon this shoulder formed by the flange 26 and by the body of the pole. piece 22. The shoulder of. the body 26 may be beveled.

A sectional view of the magnetic structure prior to final assembly is shown in FIG. 2. The dishpa-n 4 for the loudspeaker is shown in its entirety in this view. The dishpan '4 isin the nature of a truncated cone. The apex of the cone is provided with a large hole substantially concentric :with the aperture 16. The pole plate 8 oi the magnetic structure 2 may be welded to the apex portion of the dishpan 4 :at points around the large hole therein. A strip of metal 28, which projects from the side of the dishpan 4, may be provided. A terminal board (not shown) may be fastened to this projecting strip' 28.

The cross-sectional shape of the centering-compression member 24 is shown in FIG. 2 as it appears before the member 24 is compressed and loaded upon assembly of the magnetic structure 2. The bottom periphery of the member 24 rests securely in the groove 1:8 which is concentric with the aperture '16 in the pole plate 8. The groove 18 is somewhat wider thanthc thickness of the member 24 so that the member 24 may be easily inserted therein. The shape of the top surface of the member 24 may be bent in a tortuous manner, as shown, for purposes of improving the action of the compression-centering member 24 as a compression spring. In order to increase the spring torce that will be applied by the centering-compression member 24 when loaded, provisions may be made for increasing the bending moment of the top or disk portion of the member 24 about the cylindrical sides thereof. To this end, the centering-compression member 24 may be of large diameter in relation to the size of the yoke 6. The cylindrical sides of the member 24 may also be formed so that they slope inwardly very slightly.

The height of the magnet 2i and the height of the pole piece 22, taken together, is such that the pole piece 22 will extend a predetermined distance into the aperture 16 when the magnetic structure 2 is assembled. It may be observed that any magnet and any pole may be selected as a pair so long as the sum of the height of the magnet and of the pole piece are such that the pole piece will extend into the aperture by the desired distance. For example, a smaller, shorter magnet may be used with a longer pole piece. Any combination of magnet and pole piece may be selected consistent with the required magnetic characteristics for the loudspeaker. Thus, the incorporation of the present invention in a loudspeaker increases flexibility in loudspeaker design.

Upon closure of the yoke structure 6, the pole piece 22 will be advanced into the aperture 16 and the magnetic circuit including the yoke structure 6, the magnet 20 and the pole piece 22 will becompleted. The distance of this advance Will be determined by the distance of travel, in a downward direction, of the back plate 14. This distance of travel is determined by the height of the side plates 10 and 12. Thus, the height of the magnet 20 and pole piece 22 is related to the heights of the side plates 10 and 12 such that the pole piece 22 extends into the aperture 16 by the desired distance. 7

The loudspeaker magnetic structure is shown undergoing the final step in its assembly in FIG. 3. A press 30 includes a movable plunger 32 and a support 34 for holding the loudspeaker. It will be appreciated that the press 30 is shown only diagrammatically in order to simplify the description of the illustrated embodiment of the invention.

The support 34 is shaped to receive the bottom of the dishpan 4. The support 34 is provided with a centrally disposed bore adapted to receive a die 38. The upper portion of the die 38 is a hollow cylinder. The outer surface of this hollow cylinder has a diameter equal to the diameter of the aperture 16 in the pole plate 8. The upper portion of the die 38 projects into the aperture 16 and fits between the Walls of the aperture 16 and the sides of the pole piece 22; The purpose of the die 38 is to facilitate centering of the pole piece 22.

The plunger 32 of the press 31) includes a holding member 40 having a spring loaded working element 42. The working element 42 is mounted for vertical sliding movement in the holding member 44;. The working element 42 is provided with a boss 44 projecting from the surface thereof. This boss 44 is adapted to engage the back plate 14. This boss 44 is located near the side 'end of the Working element 42 and engages the free end of the back plate 14. It will be observed that the back .plate 14 is bent upon closure and pivots about the corner of the yoke structure 6 at the intersection of back plate 14 and one of the side plates 10. Thus, most eftcient utilization of forces applied by the press 36 is achieved by the application of closing pressure at the free end of the back plate 14. The working element 42 is spring loaded in order to insure that no greater than a predetermined amount of force will be applied to the back plate 14 during the closure operation. The provision of the spring loaded closing element provides further insurance against over compression of the centering-compression member 24.

The assembly of the magnetic structure may be performed in a single operation. The open yoke structure 6;, which has been previously fastened to the dishpan 4, is placedupon the support 34 in the press 3%. A guide 46 which forms part of the press 30 will be located internally of the yoke structure 6. The centering-compression member 24 may be inserted into the grooove 18.

The pole piece 22 is then dropped through the hole in the centering member and will be positioned in the aperture 16 and in the cylindrical top portion of the die 33. The magnet 20 is then inserted. The guide 46 generally .5 locates the magnet in proper position on top of the pole piece 22.

With the parts inserted, the plunger 32 of the press is brought down and closure forces are applied to the back plate 14. The dovetailed arrangement of the free ends of the side plate 12 and the back plate 14 engage so that the yoke structure 6 is permanently enclosed. Upon closure, the magnet 20 and pole piece 22 are advanced. The shoulder 26 of the pole piece 22 engages the inner rim of the centering-compression member. The centering-compression member 24 is therefore loaded and compressed upon closure. Over-compression of the centering member 24 is prevented since the distance of downward travel of the back plate 14 is limited by the height of the side plate 12 which engages the back plate 14. Thus, the magnetic structure may be assembled in one simple and convenient operation.

As an alternative procedure, the parts may be inserted and the back plate partially closed in a first operation so that the parts cannot come apart from the yoke 6. Permanent closure can be accomplished in a second operation. Thus, flexibility in manufacturing techniques is another feature of the invention. It will be noted that the number of manipulative steps may be reduced to a minimum. The anchoring of the elements in a permanent position is provided due to the forces exerted by the loaded centering-compression member 24. The centering-compression member 24 becomes locked into position against the shoulder 26 of the pole piece 22. Upon compression, the member 24 exerts spring forces thereby permanently holding the magnet 20 and the pole piece 22 permanently assembled in proper relationship. The elements of the magnetic structure 2 are also aligned in proper operating relationship. Accuracy of the size of the air gap that is defined between the cylindrical surfaces of the pole piece 22 and aperture 16 is determined by the centering-compression member 24 and insured through the use of the die 38. It has been found that the magnet 26 may be positioned other than coaxially with the pole piece 22 without affecting the proper performance of the magnetic structure. Thus, the guide 46 is merely provided for purposes of convenience of assembly.

It may be desirable, in order to more firmly lock the back plate 14 to the side plate 12, to incorporate a swaging tool in the press 30. It has been found satisfactory to swage the sides of the side plate 12 that are near the ends of the dove-tail joint. Such swaging may be applied to indent these sides of the side plate 12 to the extent shown in FIG. 1 by the dotted lines in the side plate 12.

After the magnetic structure 2 has been assembled on the press 31 it may be removed therefrom for insertion of the cone and voice coil assembly in the conventional manner.

What is claimed is:

l. A magnetic structure for a loudspeaker comprising, in combination, a magnet element having a pole end, a centering-compression member engaged with said magnet element and disposed around said pole end, a yoke of magnetic material having a pole plate and a pair of side plates, said side plates both extending in the same direction, said pole plate having an aperture therein for receiving said magnet element pole end, said centering-compression member being disposed within said yoke on said pole plate, said magnet element also being disposed within said yoke with said pole end thereof centered by said centering-compression member with respect to said pole plate aperture to define a voice coil air gap therein, and means engageable with said magnet element for advancing said pole end into said aperture and securing said magnet element and said centering-compression member in assembled relationship in said yoke which comprises a member of magnetic material providing a back plate for said yoke and movable toward said front plate into engagement with said magnet element and into assembled relationship with said side plates.

2. A magnetic structure for a loudspeaker comprising a magnet element having a pole end of lateral dimension smaller than the lateral dimension of the remainder thereof, a centering-compression member having a laterally disposed web and a longtudinally disposed flange, said web having an aperture therein of lateral dimensions larger than said pole piece lateral dimension and smaller than said remainder of said magnet element lateral dimension, said pole end being disposed in said centeringcompression member within said flange thereof and extending through said aperture in said web, a yoke of magnetic material including a pole plate having an aperture of lateral dimension slightly larger than said pole end lateral dimension, said yoke also including a pair of side plates, said centering-compression member and said magnet element being disposed within said yoke between said side plates, said flange of said centering-compression member being disposed on said pole plate of said yoke, and means engageable with said magnet element for advancing said pole end longitud nally into said pole plate aperture and securing said magnet element and centeringcompression member in assembled relationship in said yoke comprising a back plate member for said yoke disposed behind said pole plate and movable longitudinally toward said pole plate into engagement with said magnetic element and into assembled relationship with said side plates to complete a magnetic circuit through said magnet element and said yoke.

3. A magnetic structure for a loudspeaker comprising, in combination, a cylindrical magnet element having a pole end with an annular shoulder thereon, a cup-shaped centering-compression member having an aperture, a yoke of magnetic material including a pole plate having an annular aperture therein and a pair of side plates which extend in the same direction from said pole plate, said centering-compression member being disposed within said yoke on said pole plate and encompassing said pole plate aperture, said magnet element also being disposed within said yoke with said shoulder thereof disposed upon said centering-compression member and said pole end thereof extending through said centering-compression member aperture and centered by said centering-compression member with respect to said pole plate aperture, and means engageable with said magnet element for advancing said pole end into said pole plate aperture to define a voice coil air gap and also for securing said centeringcompression member and said magnet element in assembled relationship within said yoke which comprises a back plate for said yoke movable in a direction axially of said magnet element into engagement therewith and into assembled relationship with said side plates.

4. A magnetic field structure for a loudspeaker comprising, in combination, a cylindrical permanent magnet, a pole piece having an annular shoulder and disposed at one end of said permanent magnet, an annular centeringcompression member having an aperture therein, said pole piece extending through said aperture and engaging said centering-compression member at said annular shoulder, said magnet being disposed upon said pole piece and extending axially in a direction opposite to said centering member, a yoke of magnetic material having a pole plate and a pair of side plates, said side plates extending in the same direction from said pole plate, said pole plate having an aperture therein, said centering member, said pole piece and said magnet all being disposed within said yoke with said centering-compression member upon said pole plate and extending axially away from said pole plate in the same direction as said side plates, said centering member and said pole piece being disposed in centered relationship with respect to said pole plate aperture, and means engageable with said magnet for advancing said pole piece into said pole plate aperture to define a voice coil air gap therein which comprises a back plate for said yoke movable in a direction axially of said magnet into engagement with said magiet and into assembled relationship with said side plates to complete a magnetic circuit through said yoke, said magnet and said pole piece.

5. A magnetic structure for a loudspeaker comprising, in combination, a magnet element having a front end and a rear end, said front end being of smaller diameter than said rear end and having a shoulder, a centering-compression member including a spring-like web and a flange, said web having an aperture, a band of magnetic material providing a yoke having a pole plate and a pair of side plates integral with said pole plate extending in the same direction therefrom, said pole plate having an aperture, said centering member being disposed within said yoke with said flange on said pole plate and said web spaced from said pole plate, said web aperture being arranged in alignment with said pole plate aperture, said magnet element being disposed in said yoke with said shoulder on said web and said front-end extending through said web aperture in centered relationship with said pole plate aperture, and means engageable with said magnet element 'for advancing said front end of said magnet element into said pole plate aperture to define a voice coil air gap therein which comprises an integral part of said band which constitutes a back plate for said yoke, said back plate and one of said side plates defining an acute angle internally of said yoke with said back plate in engagement with said rear end or" said magnet element and in asse i-- bled relationship with the other of said pair of side plates. 6. The invention as set forth in claim wherein said pole plate has an annular groove concentric with said pole plate aperture, said annular flange of said centering-compression member being disposed Within said groove.

7. A magnetic structure comprising, a yoke of magnetic material having a pole plate, a pair of side plates, said side plates both extending in the same direction from said pole plate, and a back plate, said pole plate having an aperture nad a seat centered with respect to said pole plate aperture, a centering-compression member having an aperture centered therein, said member being disposed in said sea-t with said member aperture centered with respect to said pole plate aperture, said back plate being integral with one of said pair of side plates along one of two opposite edges of said back plate and having one or a tongue and groove in the'other of its said opposite edges, the other of said pair 'of side plates having the other of said tongue and groove along the edge thereof spaced from said pole plate, said tongue being disposed in engaging relationship within said groove to form said yoke, and a magnet having a back end in engagement with said back plate and a pole end in engagement with said member and extending through said member aperture into said pole plate aperture, said member being compremed by engagement with said magnet and permanently secured in said seat.

8. The invention as set forth in claim 7 wherein said pole plate has an annular groove concentric with said pole plate aperture providing said seat centered with respect to said pole plate aperture, wherein said compressioncenterin-g member 11% an annular edge disposed in said annular groove, and wherein said member aperture is concentric with said annular edge.

9. The method of assembling a magnetic structure for a loudspeaker having: (1) 'a yoke of magnetic material including a pole plate having an aperture, side plates extending from said pole plate, and a back plate cooperable with said side plates; (2) a magnetic element having one end positionable in said aperture; and (3) a member having an aperture and also having spring characteristics for centering said element in said pole plate aperture, comprising placing said centering member on said pole plate and between said side plates, placing said magnetic element in contact with said centering member with said one end through said centering member aperture and facing into said pole plate aperture, and then advancing said back plate into contact with the end of said element opposite said one end to force said one end into said pole plate aperture against the tension of said centering member and also into engaging relationship with at least one of said side plates.

10. The method of assembling a magnetic structure for a loudspeaker having: 1) a yoke of magnetic material including a pole plate having an aperture, side plates extending from said pole plate, and a back plate cooperable with said side plates and connected to one of said side plates; (2) a magnetic element having one end positionable in said aperture; and (3) a member having an ape ture and also having spring characteristics for centering said element in said pole plate aperture, comprising placing said centering member on said pole plate between said side plates, placing said magnetic element in contact with said centering member with said one end extending through said centering member aperture and facing into said pole plate aperture, then advancing said back plate into contact with the end of said element opposite said one end to force said one end into said pole plate aperture against the tension of said centering member, and finally engaging said back plate with the other of said side plates.

11. The method of assembling a magnetic field structure for a loudspeaker'having: (1) a yoke defined by a strip of magnetic material including a pole plate having an aperture therein, side plates extending in the same direction from said pole plate, and a back plate integral with one of said side plates along one edge thereof and extending toward said other side plate, said back plate having the opposite edge thereof spaced from said other side plate; (2) an annular centering-compression member having an aperture therein; and (3) a magnetic element having a pole piece at one end thereof cooperable with said pole plate when advanced into said pole plate aperture'to define an air gap .therein, said method comprising placing said member within said yoke, on said pole plate, and with said pole plate aperture and said centering member aperture co-axial with each other, placing said element upon said member with said pole piece extending through said centering member aperture, then pivotally bending said back plate around said one edge thereof toward said other side plate, thereby contacting said element and advancing said pole piece end thereof into said aperture against the compression of said memher, and finally engaging said back plate with said other side plate at said opposite edge of said back plate to ,close said yoke.

12. The method of assembling a magnetic field structure for .a loudspeaker having: (1) a yoke assembly including a pole plate having an aperture, a pair of side plates extending in the same direction from said pole plate, and a back plate connected integrally with one of said side plates, said side plates, said front plate and back plate being integral with each other, the other of said side plates having a groove therein, said back plate having to tongue cooperable with said groove; (2) a centeringcompression member having an aperture; 3) a permanent magnet; and (4) a pole piece having an annular shoulder, said method comprising the steps of arranging said centering-compression member within said yoke and upon said pole plate with said centering-compression member aperture in alignment with said pole plate aperture, inserting said pole piece through said centering member aperture with said shoulder thereof engaging'said centering member, placing said magnet upon said pole piece with the axis of said magnet generally paralleling said side plates and with said magnet extending above the end of said side plates, then bending said back plate with respect to said one side plate in a direction toward said front 'plate into engagement with said magnet thereby advancing gaging said tongue in said back plate and said groove in said other side plate in assembled relationship with each other.

13. The method of assembling a magnetic field structure for a loudspeaker having: (1) a yoke assembly including a pole plate having an aperture, a pair of side plates extending in the same direction from said pole plate, and .a back plate connected to one of said side plates, said side plates, said front plate and back plate being integral with each other, said pole plate having a groove around said pole plate aperture and concentric therewith; (2) a centering-compression member having an aperture concentric with the outer rim thereof; (3) a permanent magnet; and (4) a pole piece having a shoulder, said method comprising the steps of placing said centering-compression member within said yoke upon said pole plate with said rim in said groove, inserting said pole piece through said centering member aperture with said shoulder thereof engaging said centering member, placing said magnet upon 10 said pole piece with the axis of said magnet generally paralleling said side plates and with said magnet extending above the end of said side plates, then bending said back plate with respect to said one side plate in a direction toward said front plate into engagement with said magnet thereby advancing said pole piece into said pole plate aperture and compressing said centering-compression member, and finally engaging said back plate and said other side plate in assembled relationship With each other.

References Cited in the file of this patent UNITED STATES PATENTS 1,941,476 Jensen Jan. 2, 1934 2,046,515 Jensen July 7, 1936 2,174,355 Sundstrom Sept. 26, 1939 2,501,032 Harbough Mar. 21, 1950 2,524,836 Russell Oct. 10, 1950 2,666,980 Russell Jan. 26, 1954 

1. A MAGNETIC STRUCTURE FOR A LOUDSPEACKER COMPRISING, IN COMBINATION, A MAGNET ELEMENT HAVING A POLE END, A CENTERING-COMPRESSION MEMBER ENGAGED WITH SAID MAGNET ELEMENT AND DISPOSED AROUND SAID POLE END, A YOKE OF MAGNETIC MATERIAL HAVING A POLE PLATE AND A PAIR OF SIDE PLATES, SAID SIDE PLATES BOTH EXTENDING IN THE SAME DIRECTION, SAID POLE PLATE HAVING AN APERTURE THEREIN FOR RECEIVING SAID MAGNET ELEMENT POLE END, SAID CENTERING-COMPRESSION MEMBER BEING DISPOSED WITHIN SAID YOKE ON SAID POLE PLATE, SAID MAGNET ELEMENT ALSO BEING DISPOSED WITHIN SAID YOKE WITH SAID POLE END THEREOF CENTERED BY SAID CENTERING-COMPRESSION MEMBER WITH RESPECT TO SAID POLE PLATE APERTURE TO DEFINE A VOICE COIL AIR GAP THEREIN, AND MEANS ENGAGEABLE WITH SAID MAGNET ELEMENT FOR ADVANCING SAID POLE END INTO SAID APERTURE AND SECURING SAID MAGNET ELEMENT AND SAID CENTERING-COMPRESSION MEMBER 